Semiconductor device and method of manufacturing the same

ABSTRACT

A method of manufacturing a semiconductor device, including forming a capacitor above a semiconductor substrate, the capacitor including a dielectric film containing Pb, Zr, Ti and O. Forming the capacitor includes forming a crystallized film which contains Pb, Sr, Zr, Ti, Ru and O.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 10/833,096, filed Apr. 28, 2004,and claims the benefit of priority under 35 U.S.C. §119 from priorJapanese Patent Application No, 2003-318393, filed Sep. 10, 2003, theentire contents of these applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device havingcapacitors and a method of manufacturing the semiconductor device.

2. Description of the Related Art

In recent years ferroelectric memories such as ferroelectric randomaccess memories (FeRAMs) have been developed. A ferroelectric memorycomprises capacitors each having a ferroelectric film used as dielectricfilm.

A ferroelectric memory has been proposed in which the ferroelectric filmis a PZT (Pb(Zr_(x)Ti_(1−x))O₃: 0<x<1) film and the bottom electrode andtop electrode are SRO (SrRuO₃) films. (See, for example, U.S. Pat. No.6,351,006 and U.S. Pat. No. 6,194,228.) This structure can improve thefatigue characteristic of each capacitor incorporated in theferroelectric memory.

However, the elements contained in the PZT film are different from thosecontained in the SRO film, except oxygen. Therefore, electric charge islikely to accumulate in the interface between the PZT film and the SROfilm. The capacitor may therefore be deteriorated in terms of retentioncharacteristic and imprint characteristic. If the SRO film is formed bysputtering, its crystal orientation will be at random. Hence, any PZTfilm formed on the SRO film inevitably has random crystal orientation,due to the random crystal orientation of the SRO film. Accordingly, thecapacitor cannot undergo so prominent polarization as is desired.

Conventional capacitors, each having a PZT film used as ferroelectricfilm and SRO films used as electrode films, undergoes but insufficientpolarization and may be deteriorated in retention characteristic andimprint characteristic. It has been difficult to provide capacitors thatare as reliable as desired and have good characteristics.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the invention, there is provided a semiconductordevice comprising: a semiconductor substrate; and a capacitor providedabove the semiconductor substrate and including a film which containsPb, Sr, Zr, Ti, Ru and O and a dielectric film which contains Pb, Zr, Tiand O and which is provided on the film containing Pb, Sr, Zr, Ti, Ruand O.

A second aspect of the invention, there is provided a semiconductordevice comprising: a semiconductor substrate; and a capacitor providedabove the semiconductor substrate and including a dielectric film whichcontains Pb, Zr, Ti and O and a film which contains Pb, Sr, Zr, Ti, Ruand O and which is provided on the dielectric film.

A third aspect of the invention, there is provided a method ofmanufacturing a semiconductor device, comprising forming a capacitorabove a semiconductor substrate, the capacitor including a dielectricfilm containing Pb, Zr, Ti and O, wherein forming the capacitor includesforming a crystallized film which contains Pb, Sr, Zr, Ti, Ru and O.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view that schematically illustrates asemiconductor device according to an embodiment of the presentinvention;

FIGS. 2A to 2D are sectional views schematically showing, respectively,capacitors according to an embodiment of the invention;

FIGS. 3A to 3D are sectional views schematically showing, respectively,capacitors according to an embodiment of the invention;

FIGS. 4A to 4C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 5A to 5C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 6A to 6C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 7A to 7C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 8A to 8C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 9A to 9C are sectional views schematically explaining a method ofmanufacturing a capacitor according to an embodiment of the invention;

FIGS. 10A and 10B are sectional views schematically explaining a methodof manufacturing a capacitor according to an embodiment of the invention

FIGS. 11A to 11C are sectional views schematically explaining a methodof manufacturing a capacitor according to an embodiment of theinvention;

FIGS. 12A to 12C are sectional views schematically explaining a methodof manufacturing a capacitor according to an embodiment of theinvention;

FIG. 13 is a diagram representing the electrical characteristic of aPSZTR film according to an embodiment of the invention;

FIG. 14 is a diagram showing the electrical characteristic of a PSZTRfilm according to an embodiment of the invention;

FIG. 15 is a sectional view schematically depicting a capacitoraccording to an embodiment of the invention;

FIG. 16 is a diagram representing the diffraction intensity andpolarization observed with a capacitor according to an embodiment of theinvention;

FIG. 17 is a diagram representing the diffraction intensity andpolarization observed with a capacitor according to an embodiment of theinvention;

FIG. 18 is a diagram showing the X-ray diffraction pattern observed witha capacitor according to an embodiment of the invention;

FIG. 19 is a diagram representing the hysteresis of a capacitoraccording to an embodiment of the invention;

FIG. 20 is a diagram illustrating the fatigue characteristic of acapacitor according to an embodiment of the invention;

FIG. 21 is a sectional view showing a capacitor according to anembodiment of the invention;

FIG. 22 is a diagram representing the hysteresis of a capacitoraccording to an embodiment of the invention;

FIG. 23 is a diagram illustrating the fatigue characteristic of acapacitor according to an embodiment of the invention;

FIG. 24 is a sectional view showing a capacitor according to anembodiment of the invention; and

FIG. 25 is a diagram representing the hysteresis of a capacitoraccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described, with referenceto the accompanying drawings.

FIG. 1 is a sectional view that schematically illustrates asemiconductor device according to an embodiment of the presentinvention.

The semiconductor device (semiconductor integrated circuit) comprises asemiconductor substrate 1 (silicon substrate or the like) provided witha MIS transistor 2 and a capacitor 3 provided above the substrate 1. Thecapacitor 3 comprises a lower structure 10, a dielectric film 20 and anupper structure 30. The lower structure 10 includes a bottom electrode.The upper structure 30 includes a top electrode. The dielectric film 20is interposed between the lower structure 10 and the upper structure 30.An interlayer insulating film 4 or the like is provided between thesemiconductor substrate 1 and the capacitor 3. A plug 5 is formed in theinterlayer insulating film 4 and electrically connects the capacitor 3to a MIS transistor 2.

The dielectric film 20 is a ferroelectric film that contains Pb (lead),Zr (zirconium), Ti (titanium) and O (oxygen). A representative exampleof the ferroelectric film is a PZT (Pb(Zr_(x)Ti_(1−x))O₃) film. The PZTfilm may contain an element such as La (lanthanum), Sr (strontium) or Ca(calcium).

The lower structure 10 or the upper structure 30, or both, include afilm that contains Pb (lead), Sr (strontium), Zr (zirconium), Ti(titanium), Ru (ruthenium) and O (oxygen). A representative example ofthis film is a Pb_(x)Sr_((1−x))Zr_(y)Ti_(z)Ru_((1−y−z))O₃ film (where,0<x<1, 0<y<1, 0<z<1, y+z<1). It has perovskite crystal structure.Hereinafter, the film containing Pb, Sr, Zr, Ti, Ru and O will be called“PSZTR film” for the sake of convenience. The composition ratio betweenthe elements contained in the PSZTR film may be constant in thedirection of thickness of the film. Alternatively, the composition ratiomay vary in the direction of thickness of the film. The conductivity ofthe PSZTR film varies with the condition of forming the film. Hence, thePSZRT film may be a conductor in some cases, may be a dielectric in someother cases, or may include a conductive part and a dielectric part inother cases.

FIGS. 2A to 2D are sectional views schematically showing, respectively,various capacitors that may be used as capacitor 3 shown in FIG. 1.

FIG. 2A depicts a capacitor whose lower structure 10 is a PSZTR film 11.A dielectric (PZT) film 20 is formed on the PSZTR film 11, and the upperstructure 30 is formed on the dielectric film 20. In this capacitor, thePSZTR film 11 functions as bottom electrode.

FIG. 2B shows a capacitor whose lower structure 10 is a stacked filmcomposed of a PSZTR film 11 and a conductive film 12. The conductivefilm 12 contains Sr, Ru and O. Its representative example is an SRO(SrRuO₃) film. In this capacitor, at least the conductive film 12 servesas bottom electrode. The PSZTR film 11 may be a conductor in effect. Inthis case, the PSZTR film 11 functions as bottom electrode, too.

FIG. 2C illustrates a capacitor whose lower structure 10 is a stackedfilm composed of a PSZTR film 11 and a conductive film 13. Theconductive film 13 is a metal film or a metal compound film. The metalfilm can be platinum (Pt) film, iridium (Ir) film or titanium (Ti) film.The metal compound film can be iridium oxide (IrO₂) film. Hereinafter,the conductive film 13 made of metal or metal compound will be called“metal-containing film” in some cases, for the sake of convenience. Theconductive film 13 may be composed of a plurality of metal-containingfilms. In this capacitor, at least the conductive film 13 functions asbottom electrode. If the PSZTR film 11 is in effect a conductor, it willfunction as bottom electrode, too.

FIG. 2D depicts a capacitor whose lower structure 10 is a stacked filmcomposed of a PSZTR film 11, a conductive film (SRO film) 12, and aconductive film 13 (metal film or metal compound film). The conductivefilm 13 is identical to the film 13 incorporated in the capacitor ofFIG. 2C. In the capacitor shown in FIG. 2D, at least the conductivefilms 12 and 13 function as bottom electrode. The PSZTR film 11 may be,in effect, a conductor. If this is the case, the PSZTR 11 film willserve as bottom electrode, too.

FIGS. 3A to 3D are sectional views schematically depicting,respectively, capacitors 3 according to other embodiments of thisinvention.

FIG. 3A shows a capacitor whose upper structure 30 is a PSZTR film 31. Adielectric (PZT) film 20 is formed on the lower structure 10. The PSZTRfilm 31 is formed on the dielectric film 20. In this capacitor, thePSZTR film 31 functions as top electrode.

FIG. 3B illustrates a capacitor whose upper structure 30 is a stackedfilm composed of a PSZTR film 31 and a conductive film 32. Theconductive film 32 contains Sr, Ru and O. A representative example ofthe conductive film 32 is an SRO (SrRuO₃) film. In this capacitor, atleast the conductive film 32 serves as top electrode. The PSZTR film 31may be a conductor in effect. In this case, the PSZTR film 31 functionsas top electrode, too.

FIG. 3C shows a capacitor whose upper structure 30 is a stacked filmcomposed of a PSZTR film 31 and a conductive film 33. The conductivefilm 33 is a metal film or a metal compound film. The conductive film 33is similar to the conductive film 13 incorporated in the capacitor ofFIG. 2C. In the capacitor shown in FIG. 3C, at least the conductive film33 functions as top electrode. If the PSZTR film 31 is in effect aconductor, it will function as top electrode, too.

FIG. 3D depicts a capacitor whose upper structure 30 is a stacked filmcomposed of a PSZTR film 31, a conductive film (SRO film) 32, and aconductive film 33 (metal film or metal compound film). The conductivefilm 33 is similar to the film 13 incorporated in the capacitor of FIG.2C. In this capacitor of FIG. 3D, at least the conductive films 32 and33 function as top electrode. The PSZTR film 31 may be, in effect, aconductor. In this case, the PSZTR 31 film will serve as top electrode,too.

Note that the capacitors shown in FIGS. 2A to 2D are characterizedmainly by the lower structure 10, and the upper structure 30 may haveany configuration desired. On the other hand, the capacitors shown inFIGS. 3A to 3D are characterized mainly by the upper structure 30, andthe lower structure 10 may have any configuration desired. Thus, it isof course possible to combine any one of the lower structures 10 shownin FIGS. 2A to 2D with one of the upper structures 30 illustrated inFIGS. 3A to 3D.

In any capacitors shown in FIGS. 2A to 2D and FIGS. 3A to 3D, the PSZTRfilm and PZT film has main orientation direction of (111).

Some fundamental methods of manufacturing the capacitor 3 shown in FIG.1 will be described.

FIGS. 4A to 4C are sectional views schematically explaining the firstmethod of manufacturing the capacitor. First, as shown in FIG. 4A, anamorphous SRO film 15 is formed by sputtering and an amorphous PZT film25 is formed on the amorphous SRO film 15 also by sputtering. Then, theamorphous SRO film 15 and the amorphous PZT film 25 are heat-treated,reacting with each other and forming a crystallized PSZTR film 11 as isillustrated in FIG. 4B. Next, as shown in FIG. 4C, an amorphous PZT filmis formed on the PSZTR film 11 by means of sputtering or the like. Heattreatment is then performed, crystallizing the amorphous PZT film.Thereafter, an upper-structure film 30 a is formed on the PZT film 20now crystallized. Amorphous PZT films may be repeatedly deposited andcrystallized. Further, the upper-structure film may be formed before theamorphous PZT film is crystallized. In other words, the amorphous PZTfilm may be crystallized after the upper-structure film is formed.

FIGS. 5A to 5C are sectional views schematically explaining the secondmethod of manufacturing the capacitor. First, as shown in FIG. 5A, anamorphous SRO film 15 is formed by sputtering and an amorphous PZT film25 is formed on the amorphous SRO film 15 also by sputtering. Next, heattreatment is carried out, making the amorphous SRO film 15 react withthe lower portion of the amorphous PZT film 25 (particularly, thatportion of the film 25 which is close to the interface between the films15 and 25), thus forming a crystallized PZT film 11 as shown in FIG. 5B.During the heat treatment, the upper portion of the amorphous PZT film25 is crystallized, too, forming a crystallized PZT film 20. Then, asshown in FIG. 5C, an upper-structure film 30 a is formed on thecrystallized PZT film 20.

FIGS. 6A to 6C are sectional views schematically explaining third methodof manufacturing the capacitor. The steps shown in FIGS. 6A and 6B arebasically the same as those illustrated in FIGS. 5A and 5B. That is, anamorphous SRO film 15 and an amorphous PZT film 25 are formed andheat-treated, thus providing a crystallized PSZTR film 11 and acrystallized PZT film 20 a. Next, sputtering or the like is carried out,forming an amorphous PZT film on the crystallized PZT film 20 a asillustrated in FIG. 6C. Heat treatment is then performed, crystallizingthe PZT film. Thereafter, an upper-structure film 30 a is formed on thePZT film 20 b thus crystallized.

In the first to third methods described above, heat treatment convertsthe whole amorphous SRO film 15 to a PSZTR film 11. Instead, the upperand lower portions of the amorphous SRO film 15 may be converted to aPSZTR film 11 and a crystallized SRO film. In this case, such a lowerstructure 10 as depicted in FIG. 2B can be obtained. In the first tothird methods, the amorphous SRO film 15 is first formed. Alternatively,a metal film or a metal compound film is first formed and the amorphousSRO film 15 may then formed on the metal film or the metal compoundfilm. If this is the case, such a lower structure 10 as shown in FIG. 2Cor 2D can be provided.

FIGS. 7A to 7C are sectional views schematically explaining the fourthmethod of manufacturing the capacitor. First, an amorphous PZT film isformed on a lower-structure film 10 a by means of sputtering or thelike, as is shown in FIG. 7A. Then, heat treatment is performed,crystallizing the amorphous PZT film and, thus, forming a crystallizedPZT film 20, as is illustrated in FIG. 7A. Note that the PZT film 20 maybe formed by repeating a process several times, each time depositingamorphous PZT film and crystallizing the same. Next, as shown in FIG.7B, an amorphous PZT film 26 is formed on the crystallized PZT film 20and an amorphous SRO film 36 is formed on the amorphous PZT film 26.Further, heat treatment is performed, causing the amorphous PZT film 26and the amorphous SRO film 36 to react with each other, thereby forminga crystallized PSZTR film 31, as is illustrated in FIG. 7C.

FIGS. 8A to 8C are sectional views schematically explaining the fifthmethod of manufacturing the capacitor. First, a lower-structure film 10a is formed as shown in FIG. 8A. Then, sputtering or the like isperformed, forming an amorphous PZT film 26 on the lower-structure film10 a and an amorphous SRO film 36 on the amorphous PZT film 26, as isillustrated in FIG. 8B. Next, heat treatment is carried out, causing theupper portion of the amorphous PZT film 26 (particularly, the portionnear the interface with the amorphous SRO film 36) to react with theamorphous SRO film 36, thus forming a crystallized PSZTR film 31, as isillustrated in FIG. 8C. During this heat treatment the lower portion ofthe amorphous PZT film 26 is crystallized, providing a crystallized PZTfilm 20.

FIGS. 9A to 9C are sectional views schematically explaining the sixthmethod of manufacturing the capacitor. The step shown in FIG. 9A isbasically the same as the one illustrated in FIG. 7A. In this step, alower-structure film 10 a and a crystallized PZT film 20 c are formed.Next, sputtering or the like is performed, forming an amorphous PZT film26 on the PZT film 20 c and an amorphous SRO film 36 on the amorphousPZT film 26 as is illustrated in FIG. 9B. Then, heat treatment iscarried out, causing the upper portion of the amorphous PZT film 26 toreact with the amorphous SRO film 36, thereby forming a crystallizedPSZTR film 31 as shown in FIG. 9C. During the heat treatment, the lowerportion of the amorphous PZT film 26 is crystallized, too, forming acrystallized PZT film 20 d.

In the fourth to sixth methods described above, the entire amorphous SROfilm 36 is converted to a PSZTR film 31. Instead, the lower and upperportions of the amorphous SRO film 36 may be converted to a PSZTR film31 and a crystallized SRO film, respectively. In this case, such anupper structure 30 as shown in FIG. 3B can be obtained. The film finallyformed in the fourth to sixth methods is the PSZTR film 31. Nonetheless,a metal film or a metal compound film may be formed on the PSZTR film31. Alternatively, a metal film or a metal compound film may be formedon the amorphous SRO film 36 before the SRO film 36 is crystallized. Ineither case, an upper structure 30 of the type shown in FIG. 3C or 3Dcan be provided.

The first to third methods of manufacturing the capacitor are concernedmainly with the steps of forming the PSZTR film 11 and PZT film 20. Thestep of forming the upper-structure film 30 a may be replaced by anyother. The fourth to sixth methods of manufacturing the capacitor areconcerned mainly with the steps of forming the PSZTR film 31 and PZTfilm 20. The step of forming the lower-structure film 10 a may bereplaced by any other. Thus, any one of the first to third methods andany one of the fourth to sixth methods can, of course, be combined toform the capacitor.

FIGS. 10A and 10B are sectional views schematically explaining theseventh method of manufacturing the capacitor. First, as shown in FIG.10A, an amorphous SRO film 17, an amorphous PZT film 27 and an amorphousSRO film 37 are formed by sputtering or the like, one upon another inthe order they are mentioned. Then, heat treatment is performed, causingthe lower portion of the amorphous PZT film 27 to react with theamorphous SRO film 17 and causing the upper portion of the amorphous PZTfilm 27 to react with the amorphous SRO film 37. A crystallized PSZTRfilm 11 and a crystallized PSZTR film 31 are thereby formed as isillustrated in FIG. 10B. At the same time the intermediate portion ofthe amorphous PZT film 27 is crystallized, too, forming a crystallizedPZT film 20.

As indicated earlier, the upper and lower portions of the amorphous SROfilm 17 may be changed to a PSZTR film 11 and a crystallized SRO film,respectively, by means of heat treatment. Alternatively, the lower andupper portions of the amorphous SRO film 37 may be changed to a PSZTRfilm 31 and a crystallized SRO film, respectively, also by means of heattreatment. Further, a metal film or a metal compound film may be formedbeneath the PSZTR film 11. Still further, a metal film or a metalcompound film may be formed on the PSZTR film 31.

Note that the heat treatment should be performed preferably at 450 to700° C. to form a PSZTR film in the first to seventh methods describedabove.

FIGS. 11A to 11C are sectional views schematically explaining the eighthmethod of manufacturing the capacitor. An amorphous film (amorphousPSZTR film) containing Pb, Sr, Zr, Ti, Ru and O is first formed. Heattreatment is carried out, crystallizing the amorphous PSZTR film. Acrystallized PSZTR film 11 is thereby formed as shown in FIG. 11A. Then,a crystallized PZT film 20 is formed on the PSZTR film 11 as illustratedin FIG. 11B. As shown in FIG. 11C, an upper-structure film 30 a isformed on the PZT film 20. The PZT film 20 and the upper-structure film30 a may be formed by any one of the various methods described above.

FIGS. 12A to 12C are sectional views schematically explaining the ninthmethod of manufacturing the capacitor. First, a lower-structure film 10a is formed as shown in FIG. 12A. Then, a crystallized PZT film 20 isformed on the lower-structure film 10 a as is illustrated in FIG. 12B.The lower-structure film 10 a and the crystallized PZT film 20 can beformed by any one of the various methods described above. Next, anamorphous film (amorphous PSZTR film) containing Pb, Sr, Zr, Ti, Ru andO is formed on the crystallized PZT film 20. Heat treatment isperformed, crystallizing the amorphous PSZTR film. A crystallized PSZTRfilm 31 is thereby formed.

In the eighth and ninth methods, the amorphous PSZTR film can be formedby various processes such as sputtering, sol-gel process, MOCVD and thelike. If sputtering is employed, it suffices to use a target that has anadjusted composition ratio between Pb, Sr, Zr, Ti, Ru and O. It isdesirable to perform the heat treatment at 450 to 700° C. to crystallizethe amorphous PSZTR film. A crystallized PSZTR film may be formed athigh temperature, instead of crystallizing an amorphous PSZTR film. Asin the methods already described, a metal film or a metal compound filmmay be formed beneath the PSZTR film 11 or upon the PSZTR film 31.

Thus far, the patterning step included in the first to ninth methods hasnot been explained. The patterning step may be carried out after filmsconstituting the capacitor have been formed.

In the above-described embodiments, the film containing Pb, Sr, Zr, Ti,Ru and O (i.e., PSZTR film) is formed near the upper and/or lowersurface of the PZT film. The PSZTR film contains the constituentelements (Sr, Ru and O) of the SRO and the constituent element (Pb, Zr,Ti and O) of the PZT film. In the conventional capacitor, the elementscontained in the PZT film are different from those contained in the SROfilm, except oxygen, as pointed out above, the electric charge istherefore likely to accumulate in the interface between the PZT film andthe SRO film. The capacitors according to the embodiments of thisinvention are free of this problem, because the PSZTR film contains theelements constituting the PZT film. Hence, the capacitors of thisinvention would not be deteriorated in terms of retention characteristicor imprint characteristic. They can have high reliability and goodcharacteristics.

In the above-described embodiments, when the amorphous SRO film and theamorphous PZT film react with each other by the heat treatment to form acrystallized PSZTR film, the PSZTR film near the PZT film can have asimilar composition to that of the PZT film. That is, the portion of thePSZTR film, which is nearer the PZT film can have a composition moresimilar to that of the PZT film than any other portion. Continuitybetween the PSZTR film and the PZT film can therefore be ensured. Thiscan minimize the above-mentioned problem.

Examples of the embodiments of the present invention will be describedbelow.

EXAMPLE 1

First, an amorphous SRO film (0 to 10 nm thick) was formed on a Ptsubstrate by means of sputtering. Then, an amorphous PZT film (0 to 30nm thick) was formed on the amorphous SRO film by sputtering, too. TheZr/Ti ratio (in number of atoms) in the amorphous PZT film was 40/60 or30/70. Further, RTA (Rapid Thermal Annealing) was performed at 600 C for30 seconds. During this heat treatment the amorphous SRO film and theamorphous PZT film reacted with each other, forming a crystallized PSZTRfilm.

FIGS. 13 and 14 are diagrams that represent the electricalcharacteristics (resistances) of PSZTR films thus formed. The resistanceof PSZTR film was measured by two-probe method. To be more specific, thetwo probes were set in contact with the Pt substrate and the PSZTR film,respectively, and the resistance between the probes was detected.

FIG. 13 shows the measuring results obtained of PSZTR films which wereidentical in the thickness of the amorphous PZT film, i.e., 10 nm, butdifferent in the thickness of the amorphous SRO film. As FIG. 13reveals, the thicker the amorphous SRO film, the lower the resistance,and the resistance is almost constant if the amorphous SRO film is 2 nmor more thick.

FIG. 14 depicts the measuring results obtained of PSZTR films which wereidentical in the thickness of the amorphous SRO film, i.e., 2.5 nm, butdifferent in the thickness of the amorphous PZT film. As FIG. 14indicates, the resistance is almost proportional to the thickness of theamorphous PZT film. The resistance that the PSZTR film has when theamorphous PZT film is 30 nm thick is almost equal to the resistance of aPZT film (10 nm thick) that has been crystallized without forming an SROfilm.

The measuring results of FIGS. 13 and 14 teach that a PSZTR film isformed as the elements contained in the SRO film diffuse into the PZTfilm and the elements of the PZT film diffuse into the SRO film duringthe heat treatment. Due to this mutual diffusion, the concentrations ofSr and Ru gradually decrease toward the upper surface of the PSZTR film,and the concentrations of Pb, Zr and Ti gradually decrease toward thelower surface of the PSZTR film. The resistance of the PSZTR filmvaries, depending upon its composition.

The surfaces of the PSZTR films thus formed were observed with a SEM(Scanning Electron Microscope). Of these PSZTR films crystallized, anyformed by heat-treating only an amorphous SRO film had foreign-matterparticles of sizes ranging from 1 μm to 10 μm. These particles areconsidered to be of ruthenium dioxide, strontium oxide, and strontiumcarbonate generated as amorphous SRO. reacts with carbon dioxidecontained in the air. Of the PSZTR films crystallized, any formed byheat-treating an amorphous SRO film and an amorphous PZT film had noforeign-matter particles. Such foreign-matter particles render thedevice defective. Thus, the use of a PSZTR film in place of an SRO filmcan help to enhance the yield of the device.

EXAMPLE 2

Using a Ti film as seed layer, a Pt film was formed on a semiconductorwafer by sputtering to a thickness of 100 nm. An amorphous SRO film wasthen formed on the Pt film by sputtering, too. Further, an amorphous PZTfilm was formed on the SRO film by means of sputtering. Note that theamorphous PZT had a Zr/Ti composition ratio of 30/70. RTA was performedon the resultant structure at 600° C. for 30 seconds. During this heattreatment, the amorphous SRO film and the amorphous PZT film reactedwith each other, forming a crystallized PSZTR film. An amorphous PZTfilm was then formed by sputtering. The resultant structure wassubjected to heat treatment (RTA), at 600° C. for 30 seconds. Theamorphous PZT film was thereby crystallized. Another amorphous PZT wasthen formed and crystallized in the same conditions. The PSZTR film andthe PZT films, thus formed, had a total thickness of about 70 nm.

Next, an amorphous SRO film having a thickness of 10 nm was formed onthe PZT film, by means of sputtering. A Pt film having a thickness of 50nm was formed on the amorphous SRO film, also by sputtering. Theresultant structure was subjected to heat treatment (RTA) at 600° C. for30 seconds, thereby crystallizing the amorphous SRO film. Thereafter,the structure underwent recovery annealing in an electric furnace, at600° C. for one hour.

As a result, a capacitor was manufactured. As FIG. 15 shows, thecapacitor comprised a Pt film 101, a PSZTR film 102, a PZT film 103, anSRO film 104 and a Pt film 105.

FIGS. 16 and 17 are diagrams that represent the (222) diffractionintensity and polarization Qsw of capacitors of the type illustrated inFIG. 15. FIG. 16 shows the measurement result of the capacitors whichwere identical in the thickness of the amorphous PZT film, i.e., 10 nm,but different in the thickness of the amorphous SRO film. FIG. 17 showsthe measurement result of the capacitors which were identical in thethickness of the amorphous SRO film, i.e., 2.5 nm, but different in thethickness of the amorphous PZT film.

As FIGS. 16 and 17 show, when the (222) intensity is high, that is thedegree of the orientation of (111) direction of the PZT film is high,the polarization Qsw is large. As seen from FIG. 16, the polarizationQsw is large if the amorphous SRO film is about 2.5 nm or less thick. AsFIG. 17 reveals, the polarization Qsw is large if the amorphous PZT filmhas a thickness ranging from about 10 nm to about 20 nm. In view ofthis, it is desired that the amorphous SRO film be 2.5 nm or less thickand that amorphous PZT film be 10 to 20 nm thick. The polarization Qswdoes not greatly decrease even if the amorphous SRO film is about 10 nmthick. Hence, the amorphous SRO film may have a thickness of 10 nm orless. Moreover, the amorphous PZT film may have a thickness of 30 nm orless, because the polarization Qsw does not much decrease even if theamorphous PTZ film is about 30 nm thick. Note that the averagecomposition of the PSZTR film isPb_(0.8)Sr_(0.2)Zr_(0.24)Ti_(0.56)Ru_(0.2)O₃ if the amorphous SRO andamorphous PZT films are 2.5 nm and 10 nm thick, respectively.

EXAMPLE 3

The lower structure of a capacitor was formed in the same way as inExample 2. The amorphous SRO film was 2.5 nm thick, and the amorphousPZT film was 10 nm thick. Heat treatment was carried out at 650° C. toform a PSZTR film. The PZT film exhibited Zr/Ti composition ratio of40/60. After the PSZTR film was formed, an amorphous PZT film was formedby sputtering, to a thickness of 30 nm. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. The amorphous PZT film wasthereby crystallized. Then, another amorphous PZT film was formed andcrystallized in the same condition as the first PZT film. The PSZTR filmand PZT films thus formed had a total thickness of about 70 nm. Theaverage composition of the PSZTR film wasPb_(0.8)Sr_(0.2)Zr_(0.32)Ti_(0.48)Ru_(0.2)O₃.

Next, an amorphous SRO film was formed on the PZT film by means ofsputtering to a thickness of 10 nm. A Pt film was formed on the SRO filmby sputtering, to a thickness of 50 nm. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. The amorphous SRO film wasthereby crystallized. The structure was subjected to recovery annealingin an electric furnace, at 650° C. for one hour. A capacitor of thestructure shown in FIG. 15 was manufactured.

FIG. 18 is a diagram that shows the X-ray diffraction pattern observedwith the capacitor thus manufactured. As seen from FIG. 18, theorientation direction of the Pt film is (111), and the main orientationdirection of the PZT film is (111). Hence, the main orientationdirection of the lower structure, dielectric film and upper structure ofthe capacitor is (111).

FIG. 19 is a diagram that represents the hysteresis of a capacitordescribed above. The capacitor exhibited a good hysteresis curve at themeasuring voltage of 1.5 V. The polarization Qsw was about 22 μC/cm².FIG. 20 is a diagram that illustrates the fatigue characteristic of thecapacitor. The fatigue characteristic remained good, even afterdata-writing/reading was repeated over 10⁸ times on the capacitor. Thismeans that the capacitor excels in reliability.

EXAMPLE 4

A Pt film was formed on a semiconductor wafer by sputtering, to athickness of 100 nm. An amorphous SRO film was formed on the Pt film bysputtering, too, to a thickness of 10 nm. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. During the heat treatmentthe amorphous SRO film was crystallized.

Next, a Ti film, an amorphous PZT film, an amorphous SRO film and a Ptfilm, which were 2.5 nm, 70 nm, 10 nm and 50 nm thick, respectively,were formed by sputtering, one upon another in the order they arementioned. The resultant structure was subjected to RTA at 650° C. for30 seconds. During this heat treatment, the upper portion of theamorphous PZT film reacted with the amorphous SRO film, forming acrystallized PSZTR film. During the heat treatment, too, the lowerportion of the amorphous PZT film was crystallized. The resultantstructure was subjected to recovery annealing in an electric furnace, at650° C. for one hour.

As a result, a capacitor was manufactured. As FIG. 21 shows, thecapacitor comprised a Pt film 111, an SRO film 112, a PZT film 113, aPSZTR film 114 and a Pt film 115.

FIG. 22 is a diagram that represents the hysteresis of the capacitorthus manufactured. The capacitor exhibited a good hysteresis curve atthe measuring voltage of 1.5 V. The polarization Qsw was about 30μC/cm². FIG. 23 is a diagram that depicts the fatigue characteristic ofthe capacitor. The fatigue characteristic remained good, even afterdata-writing/reading was repeated over 10⁸ times on the capacitor. Thismeans that this capacitor, or Example 4, excels in reliability, too.

EXAMPLE 5

The lower structure of a capacitor was formed in the same way as inExample 2. The amorphous SRO film was 2.5 nm thick, and the amorphousPZT film was 10 nm thick. Heat treatment was carried out at 650° C. toform a PSZTR film. The PZT film had Zr/Ti composition ratio of 40/60.After the PSZTR film was formed, an amorphous PZT film was formed bysputtering, to a thickness of 25 nm. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. The amorphous PZT film wasthereby crystallized. Then, another amorphous PZT film was formed andcrystallized in the same condition as the first PZT film.

Then, an amorphous PZT film, an amorphous SRO film and a PT film, whichwere 10 nm, 2.5 nm and 50 nm thick, respectively, were formed bysputtering, in the order they are mentioned. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. During this heat treatmentthe amorphous PZT film and the amorphous SRO film reacted with eachother, forming a crystallized PSZTR film. The resultant structure wassubjected to recovery annealing in an electric furnace, at 650° C. forone hour.

A capacitor was thereby manufactured which had the structure shown inFIG. 24. As FIG. 24 shows, this capacitor comprised a Pt film 121, aPSZTR film 122, a PZT film 123, a PSZTR film 124 and a Pt film 125.

FIG. 25 is a diagram that represents the hysteresis of the capacitorthus manufactured. The capacitor exhibited a good hysteresis curve atthe measuring voltage of 1.5 V. The polarization Qsw was about 13μC/cm². This capacitor excels in characteristics, too.

COMPARATIVE EXAMPLE

A Pt film was formed on a semiconductor wafer by sputtering, to athickness of 100 nm. An amorphous SRO film was formed on the Pt film bysputtering, too, to a thickness of 10 nm. The resultant structure wassubjected to RTA at 650° C. for 30 seconds. During the heat treatmentthe amorphous SRO film was crystallized. Next, a Ti film and anamorphous PZT film, which were 2.5 nm and 35 nm thick, respectively,were formed by sputtering, in the order they are mentioned. Theresultant structure was subjected to RTA at 650° C. for 30 seconds.During this heat treatment, the amorphous PZT film was crystallized.Another amorphous PZT was formed and crystallized in the sameconditions. Next, an amorphous SRO film and a Pt film, which were 10 nmand 50 nm thick, respectively, were formed by sputtering, in the orderthey are mentioned. The structure was subjected to RTA at 650° C. for 30seconds. This heat treatment crystallized the amorphous SRO film. Theresultant structure was subjected to recovery annealing in an electricfurnace, at 650° C. for one hour. A capacitor was thereby manufactured.

The X-ray diffraction pattern of the capacitor thus made was examined.The examination showed that the orientation direction of the PZT filmwas at random. The capacitor was examined for its hysteresis, too. Thecapacitor was found to exhibit no good hysteresis. The polarization wasinsufficient. The comparative example could not attain goodcharacteristics, probably because it had no PSZTR film at all.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the sprint or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method of manufacturing a semiconductor device, comprising forminga capacitor above a semiconductor substrate, the capacitor including adielectric film containing Pb, Zr, Ti and O, wherein forming thecapacitor includes forming a crystallized film which contains Pb, Sr,Zr, Ti, Ru and O.
 2. The method according to claim 1, wherein formingthe crystallized film which contains Pb, Sr, Zr, Ti, Ru and O comprises:forming an amorphous film which contains Sr, Ru and O; forming anamorphous film which contains Pb, Zr, Ti and O, on the amorphous filmwhich contains Sr, Ru and O; and causing at least an upper portion ofthe amorphous film containing Sr, Ru and O to react with at least alower portion of the amorphous film containing Pb, Zr, Ti and O.
 3. Themethod according to claim 1, wherein forming the crystallized film whichcontains Pb, Sr, Zr, Ti, Ru and O comprises: forming an amorphous filmwhich contains Pb, Zr, Ti and O; forming an amorphous film whichcontains Sr, Ru and O, on the amorphous film which contains Pb, Zr, Tiand O; and causing at least a lower portion of the amorphous filmcontaining Sr, Ru and O to react with at least an upper portion of theamorphous film containing Pb, Zr, Ti and O.
 4. The method according toclaim 1, wherein forming the crystallized film which contains Pb, Sr,Zr, Ti, Ru and O comprises: forming an amorphous film which contains Pb,Sr, Zr, Ti, Ru and O; and crystallizing the amorphous film whichcontains Pb, Sr, Zr, Ti, Ru and O.